When bonding semiconductor chips or the like to bonding pads, it has been common practice to utilize solder preforms to provide adherence and desirable heat transfer characteristics to the assembly. Furthermore, to facilitate handling, a lead frame assembly of, say, forty bonding pads and associated electrical leads may be fabricated as a single assembly, ready for application of the elements to be bonded thereto. Such an assembly is shown in FIG. 1. In order to bond semiconductor chips, for example, to the plurality of bonding pads 12 of FIG. 1, preform solder elements are placed on each bonding pad together with the chips and this plurality of "sandwiches" is heated, preferably in a furnace, to cause adherence of each chip to its respective bonding pad.
The system, as described above, presents some problems in practice: (1) The solder preforms must be larger than necessary to assure total coverage of the chip contact area due to positioning tolerances in placement of the parts of the assembly, (2) the solder preforms may be unknowingly dislodged from the "sandwich" during the process with the result that the chip is not soldered to its corresponding bonding pad, and (3) there is no assurance that the chip will be maintained in a desired position with respect to its bonding pad because of the "float" effect of the molten solder.
Some manufacturers may use manual systems for tinning the bonding pad but these operations are very slow, and, thus, relatively expensive.